Field of the Invention
The present invention relates to an imaging apparatus that captures optical coherence tomographic images.
Description of the Related Art
Imaging apparatuses that employ optical coherence tomography (hereinafter referred to as OCT) are being developed (hereinafter, an imaging apparatus that employs OCT is referred to as an OCT apparatus). An OCT apparatus irradiates an object with light while changing the wavelength of the irradiation light, makes reflection light beams returned from different depths of the object interfere with reference light, and analyzes frequency components contained in the intensity of the resulting interference light (that is, the interference spectrum) to thereby obtain a tomographic image of the object. OCT apparatuses are used in fundus examinations, for example.
In fundus examinations, it is basically desirable to find any lesion located away from the macula in order to detect ocular diseases earlier and to start a treatment. To meet such a desire, OCT apparatuses used in fundus examinations are also expected to have a wider angle of view currently.
To attain the wider angle described above, Japanese Patent Laid-Open No. 2012-115578 discloses a typical configuration of a swept-source OCT (SS-OCT) apparatus as described above having a typical sample rate and a technique for creating a tomographic image of a wide area by combining together a plurality of tomographic images to widen the area of the fundus which is observable on the tomographic image. Although an expensive swept light source that can generate light having a long coherence length and an expensive analog/digital (A/D) converter having a wide analog band need not be used according to Japanese Patent Laid-Open No. 2012-115578, image processing for combining together the plurality of tomographic images takes longer and is troublesome, which is a shortcoming.
Although Japanese Patent Laid-Open No. 2014-016181 does not address the above-described issue concerning the wider angle of view, it illustrates a configuration in which two A/D converters are used while switching between the two A/D converters is performed to implement an interleaving operation, for example, in order to configure an OCT apparatus. However, Japanese Patent Laid-Open No. 2014-016181 only illustrates the configuration for implementing an interleaving operation and does not indicate that this configuration is used to address an issue concerning comprehensively obtaining, with a single operation, a tomographic image in a depth range associated with a wider angle. Moreover, Japanese Patent Laid-Open No. 2014-016181 does not disclose a method for correctly maintaining an equal wavenumber property of the sampling timing required for SS-OCT in the process of transmitting the clock.